Audience

In a way, every
aspect of writing has to do with audience because you're trying
to communicate something to someone else, and how good your
writing is has to do with how well you accomplish that. Of course, different kinds of audiences exist, and they
need and are interested in different things. You would describe
yourself differently, for instance, in a letter to a pen-pal in a
foreign country, in a job application, and in a classified
personal ad in the newspaper. Audience also has to do with the
vocabulary you use, whether you're writing for lay people or
experts, what assumptions you share with your readers, and what
tone you use.